کاغذ کادو چهارضلعی

Main.cpp

#include <iostream>
#include <math.h>
#include <string>
#include <cmath> 
#include <iomanip> 
#include <iostream> 
using namespace std;

int main()
{
    long double a, b, c, d;
    cin >> a >> b >> c >> d;
    
    long double s = (a + b + c + d)/2;
    cout << setprecision(12) << sqrt((s-a)*(s-b)*(s-c)*(s-d));
    
    return 0;
}